Seasonal water quality trends in a tailwater recovery system in the Mississippi Delta

Abstract

In the Mississippi Delta region, tailwater recovery (TWR) systems are an important best management practice to address both water quality and quantity issues. TWRs are surface water capture-and-irrigation reuse systems using a combination of a ditch to capture surface water, an on-farm storage (OFS) reservoir to store captured surface water, and pumps to move surface water from the ditch into the OFS reservoir and to irrigate nearby fields. To determine if TWR systems are an effective way to reduce water use and downstream nutrient loads, water quality and quantity data from a ditch and pond TWR system in Sunflower County, Mississippi, were measured for five years. Objectives of this study were to assess seasonal TWR system runoff and runoff water quality trends. All water quality parameters had clear seasonal variation, except for chlorophyll a. Dissolved oxygen (DO), solids, conductivity, total dissolved organic carbon (TDOC), total phosphorus (TP), and total Kjeldahl nitrogen (TKN) exhibited significant differences between OFS reservoir and ditch sites. Total solids were 2 to 4 times higher in the ditch than in the reservoir, depending on the season, indicating sediment lost from fields through runoff is not necessarily returned to the fields via irrigation from the reservoir. Nutrients were also generally higher in the ditch than in the reservoir. Phosphate (PO₄) was 1.4 times higher in the ditch in spring compared to the reservoir, while ammonium (NH₄) and nitrate (NO₃) were 2 to 4 times higher in the ditch during the summer. These results suggest the reservoir serves an important function to process nutrients and sediments through settling, biological uptake of nutrients, and biogeochemical transformations and emphasizes the importance of a closed TWR system.